A wind tunnel study of aerodynamic effects of façade and roof greening on air exchange from a cubic building

Abstract

Ventilation through openings has long been considered an effective means of improving indoor air quality in living spaces. Although green roofs and façade greening are wide spread for urban buildings, their effect on ventilation is not yet fully understood. This paper presents a fundamental experimental investigation of the relevant aerodynamic effect on the air exchange of an isolated building exposed to wind. The study was performed in an atmospheric boundary layer wind tunnel using a reduced scale (M = 1:300) cubic model building exposed to 0° wind with openings on its two side faces. Vegetation of different permeabilities, heights and thicknesses were placed on the building, and tracer gas measurements were performed. These properties may correspond to different vegetation species e.g ivy or shrubby plants, commonly used for façade or rooftop greening. Experimental results show that, regardless of species, façade greening on the windward wall attenuates air exchange rate while rooftop greening enhances it, especially at the upper building levels. When applying façade or rooftop greening of the same properties, the building’s air exchange rate is reduced by up to 16% but increases by only up to 8%, respectively. The effect of vegetation thickness is more evident for the thicker layers of façade greening. It is notable however, that a layer of low-permeability facade greening has a minor influence on air exchange rate.